black rat snake vs blacksnake

black rat snake and blacksnake both are nouns.

Word	Noun	Adjective	Verb	Adverb
black rat snake	Yes	No	No	No
blacksnake	Yes	No	No	No

As nouns, black rat snake and blacksnake are synonyms defined as:

black rat snake and blacksnake: large harmless shiny black North American snake

Other synonyms of black rat snake include Elaphe obsoleta, mountain blacksnake, pilot blacksnake.

black rat snake (noun)	blacksnake (noun)
large harmless shiny black North American snake	blackish racer of the eastern United States that grows to six feet
	large harmless shiny black North American snake